I'm doing something similar with a Joomla site. That site is pretty small, I would just copy the html (by right clicking and hitting view source) for each page and start putting it into a SS project. I'd probably start by creating a page type for each page and create its associated template. From there you can start writing in any functionality that the page type requires. For example the home page would need some functions to handle the contact form, perhaps an image upload area in the cms for a banner image, the ability to go and get 'blog' posts so you can populate that news and articles area with a 'blog' that links to a more detailed 'blog post'.